Phosphor coatings for lighting applications typically require a binder phase in the phosphor suspension to obtain adequate phosphor adherence to the lamp envelope. One such commonly used binder is Aluminum Oxide C (AOC) which is a gamma phase aluminum oxide having a particle size on the order of 20 nanometers. While this material effectively promotes phosphor adherence, it does not contribute to the light output of the lamp and is a strong absorber of vacuum ultraviolet (VUV) radiation.
Other nanophase materials such as Y2O3:Eu and SiO2 have been evaluated as alternatives to Aluminum Oxide C in phosphor systems for VUV applications, particularly neon gas discharge lamps. These materials are described in copending applications Ser. Nos. 09/162,192 and 09/483,435. While these materials promote phosphor adherence, neither material was shown to emit visible light under VUV excitation and only the nanophase Y2O3:Eu exhibited a weak visible emission under ultraviolet (UV) excitation. As such, neither material is able to contribute to the light output of a lamp which relies primarily on VUV excitation of the phosphor.
Thus, it would be an advantage to provide a nanophase binder material which emits visible light under both UV and VUV excitation.
It is an object of the invention to obviate the disadvantages of the prior art.
It is another object of the invention to provide a binder which promotes adherence in phosphor coatings and which emits visible light under UV and VUV excitation.
It is a further object of the invention to provide a method for coating a lamp in which the binder may be added directly to the phosphor coating suspension.
In accordance which an object of the invention, there is provided a luminescent nanophase binder comprising nanoparticles of a luminescent glass which emit visible light under UV and VUV excitation. In one aspect of the invention, the luminescent nanophase binder comprises SiO2 nanoparticles doped with terbium or terbium and yttrium.
In accordance with another object of the invention, there is provided a method for coating a lamp comprising forming a colloidal dispersion of SiO2 nanoparticles doped with terbium or terbium and yttrium, combining the colloidal dispersion with a suspension of a phosphor, coating the suspension on the lamp, drying the coating, and firing the coating at a temperature sufficient to remove water and residual organic material.